The present invention relates to closures for bottles and, in particular, to the type of stopper useful with wine bottles.
It is known to manufacture articles from foamed plastic by injection or extrusion of polyurethane, polystyrene or polyolefin. In the case of injection molding, the grains of plastic material are generally mixed with a pore-forming additive or blowing agent which decomposes at a predetermined temperature, freeing a gas which stays trapped as bubbles in the molded article, forming a closed, cellular or honeycomb structure. Such articles, in particular those formed from polyethylene, have an outer layer in which the pores are of small size, while the density occurring in regions away from the injection point is much greater than that around the injection nozzle.